1. Field of the Invention
The present invention relates to a gas sensor unit constituting an assembly of a gas sensor having a gas detecting element and a sensor cap fitted thereon for transmitting an output signal from the gas sensor to an external device, as well as the sensor cap alone.
2. Description of the Related Art
Various types of gas sensors having a gas detecting element have hitherto been proposed. One example is a gas sensor having a gas detecting element formed from an oxygen-ion conductive zirconia ceramic, and which is mounted on an exhaust gas pipe of an internal combustion engine so as to detect the oxygen concentration in the exhaust gas (e.g., Japanese Utility Model Publication No. 53-95884 (published in 1978) and Japanese Utility Model Publication No. 53-95886 (published in 1978)).
3. Problems to be Solved by the Invention
The gas sensors of Japanese Utility Model Publication No. 53-95884 and Japanese Utility Model Publication No. 53-95886 have a bottomed tubular gas detecting element and a tubular sensor terminal for outputting an output signal from the gas detecting element outside the sensor. These gas sensors are formed such that the output signal is transmitted outside the sensor (e.g., to an ECU) through a connection terminal connecting to the sensor terminal, a reference gas (outside air) is introduced to the inside of the gas detecting element through a tubular interior of the sensor terminal, and the tubular interior of the sensor terminal and the inside of the gas detecting element are ventilated.
In this type of gas sensor in which the sensor terminal is connected to the connection terminal to transmit an output signal, there are cases where a sensor cap is required which has a cap-like enclosing member for covering the connection terminal (cap terminal) and the sensor terminal for the purpose of protecting the sensor terminal and connection to the sensor terminal.
With such a sensor cap, there are cases where a communicating hole between the outside and an internal space must be provided to speedily ventilate the internal space of the gas sensor and the sensor cap. The purpose thereof is to introduce a reference gas from outside the sensor and to prevent an abnormal change in reference gas concentration (due to generation gas from a foreign object which has entered the interior of the gas sensor or the interior of the sensor cap), as well as to prevent corrosion and the like of the sensor terminal and the cap terminal.
Meanwhile, there are also cases where, in order to prevent short-circuiting, corrosion and the like of the sensor terminal and the cap terminal due to entry of water droplets and the like into the internal space from outside the sensor, the internal space must be made watertight.